Typically, a fully charged battery provides less than eight hours of operating time and then requires eight hours to recharge. If a customer allows the battery to cool after charging for eight hours, as recommended by the manufacturers, each battery can only be used for a single eight-hour shift per day. As a result, users who want the benefits of electric vehicles, but need to operate more than one shift need elaborate battery handling equipment and “battery rooms” where batteries can be changed and charged outside the vehicle to permit these vehicles to be used for consecutive eight hour shifts.
Fast or opportunity charging allows a battery-powered industrial vehicle to continue operating longer and for more total hours than conventional battery charging. For example, instead of a fork lift truck in a warehouse having to go offline to switch battery packs at regular intervals, one pack charges while the other is used, the battery pack stays in the truck and can stay in operation with charging occurring during employee breaks and other lulls in activity. This translates into higher productivity. Additionally, fast charging eliminates the need for battery changing and thus the capital costs of extra batteries, battery changing equipment, floor space, and racking. Eliminating battery changing also reduces operating expenses by reducing the need for trained operators for these changing and charging activities.
Fast charging improves energy efficiency and reduces energy costs, because the fast chargers themselves are more efficient than non fast/opportunity charging chargers and because opportunity charging with less frequent overcharging increases the coulombic and energy efficiency of the battery. Additionally, opportunity charging with a fast charger can keep the battery at a higher average state of charge, which helps to increase lift truck performance and speed. Operating at a higher state of charge (SOC) also reduces maintenance costs that are correlated with the higher currents and component temperatures encountered during low voltage/SOC operation.
Although fast or opportunity charging provides a number of benefits, it also poses some challenges. Chargers used for fast or opportunity charging operate at much higher current levels than traditional systems and thus require connectors and cables capable of handling higher current loads. Additionally, these connectors need to be easy to connect and disconnect during use and should be easy to assemble and maintain.